Methoxy poly(ethylene oxide)-b-poly(ethyl cyanoacrylate) (mPEG-b-PECA), amphiphilic block copolymer, was synthesized via oxyanion-initiated polymerization with a sodium alcoholate-terminated monomethoxy poly(ethylene glycol) as the macroinitiator. mPEG-b-PECA was characterized by GPC, 1H-NMR and FTIR. The results indicate that the structure of mPEG-b-PECA is well controlled with narrow molecular weight distribution. The dexamethasone (DXM)-loaded mPEG-b-PECA nanoparticles (NPs) were prepared by the nanoprecipitation technique and characterized by LPSA, 1H-NMR and TEM. The DXM-loaded mPEG-b-PECA NPs are of spherical shape with the size of less than 100 nm. The drug-loaded amount (DL) and encapsulation efficiency (EE) of DXM-loaded NPs were investigated by HPLC. The results show that DXM can be effectively incorporated into mPEG-b-PECA NPs, which provides a potential delivery system for DXM and other hydrophobic drugs. Methoxy poly (ethylene oxide) -b-poly (ethyl cyanoacrylate) (mPEG-b-PECA), amphiphilic block copolymer, was synthesized via oxyanion- initiated polymerization with a sodium alcoholate-terminated monomethoxy poly (ethylene glycol) as the macroinitiator. MPEG -b-PECA was characterized by GPC, 1H-NMR and FTIR. The results indicate that the structure of mPEG-b-PECA is well controlled with narrow molecular weight distribution. The dexamethasone (DXM) -loaded mPEG-b-PECA nanoparticles NPs) were prepared by the nanoprecipitation technique and characterized by LPSA, 1H-NMR and TEM. The DXM-loaded mPEG-b-PECA NPs are of spherical shape with the size of less than 100 nm. The drug-loaded amount (DL) and encapsulation efficiency (EE) of DXM-loaded NPs were investigated by HPLC. The results show that DXM can be effectively incorporated into mPEG-b-PECA NPs, which provides a potential delivery system for DXM and other hydrophobic drugs.